Not Applicable.
Not Applicable.
More specifically, the invention relates to a cutting tool having at least one cutting blade which is attachable to a holder body and, while the cutting tool rotates relative to a workpiece, gets into a chip-cutting engagement with a workpiece if the holder body or workpiece undergoes a linear feed motion at the same time.
A typical example for such a cutting tool is a surface-milling cutter or cornering cutter which, for example, is loaded with reversible cutting blades. The reversible cutting blades typically are uniformly mounted on the circumference of the holder body in a predetermined pitch.
Reversible cutting blades are commonly used on such tools, but also on specific drilling tools, reamers or the like. Another application is the one for lathe tools. The invention which will be explained below, however, is not limited to using reversible cutting blades although substantial reference is made thereto for the purposes of explanation.
Reversible cutting blades are commonly loaded either directly into appropriate pockets of the holder body in a known manner or use so-called cassettes which, in turn, are fixed in pockets of the holder body.
The positioning of the cutting edge relative to the axis of the holder body is of significance for the way of action of such a cutting tool, e.g. a milling cutter. The determining factors are the axial angle, the radial angle, and the setting angle. The axial angle means the relative position of a cutting blade or its edge with respect to the axis of rotation of the milling cutter body. The radial angle is the angle between the plane of the milling blade and a radius of the holder body. The setting angle is the angle which the cutting edge has with respect to the direction of tool feed. All of the angles usually are unlike 90xc2x0. For obvious reasons, efforts are made not to allow the cutting edge to engage the workpiece simultaneously across the whole length of the cutting edge, but gradually while starting from one end. This minimizes the stress acting on the cutting blade and the cutting edge, and the vibrations which naturally occur because of cutting blade bumps while metal-cutting is done with several blades.
A series of parameters play a role while metal-cutting is done with the cutting tools described. The desirable feature is a large stock removal per unit time at a minimal stress of the cutting edge and a minimum of cutting force. The cutting force naturally has an effect on energy consumption during a metal-cutting operation. High stresses acting on the cutting edge result in short tool service lives and, hence, cause replacing operations which are time-consuming and have an impact on the entire time of manufacture. Further, the expenditure in manufacture is influenced by the different conditions in using cutting blades. In the conventional metal-cutting technique, the cutting blades are identically positioned and oriented on the holder body so that only certain areas of a cutting edge are subjected to a particular stress in most cases. As soon as the most stressed area of the cutting edge has ceased to be usable the cutting blades requires to be exchanged or reversed. The result is that the cutting blade is incompletely utilized.
It is known to achieve a dampening action by arranging the cutting blades at a differing pitch on the circumference of the holder body.
EP 0 480 576 and EP 0 585 871 have made known reversible cutting blades in which the cutting edges are broken up into cutting edge portions between which there is a step each. The cutting edge portions ascend like a ramp between the steps and the arrangement is such as to cause the cutting edge portions to overlap in the stepped area. Efforts are made to avoid or minimize chatter and to produce separate metal-cutting portions here. The setting angle is constant for the known cutting blades over the length of their cutting edge.
EP 0 814 932 has made known a cutting blade in which the cutting edge is also broken up in stepped cutting edge portions with the transition point of the steps being chosen so as to form an obtuse angle. Furthermore, the cutting edge portions are situated on the surface area of an imaginary cylinder. The known cutting blade is intended to improve the chip-breaking characteristic, to reduce the cutting force, and to minimize wear.
It is the object of the invention to improve a cutting tool of the generic type in a way such as to minimize the cutting force and to obtain a larger stock removal with the machine performance remaining the same. Furthermore, it is intended to be an object to improve the utilization of the cutting edges.
The cutting depth is determined by the rate at which the cutting tool or the workpiece is fed in the machine. In conventional cutting tools, the feed motion is such that the larger area gets into engagement with the workpiece over the length of the continuous cutting edge. In the invention, however, only single portions each of the cutting edge of a cutting blade will get into engagement with the workpiece. In the inventive cutting tool, the at least one cutting edge is also subdivided into stepped portions. The fact essential to the invention, however, is that the setting angle of the cutting edge portions differs. Thus, the invention provides a subdivision in cutting with respect to the cutting edge employed and, by doing so, can vary the setting angle on the tool so as to make it engage differently depending on the position of the cutting edge portion. As is known the xe2x80x9clowermostxe2x80x9d end portion of a cutting edge is most subjected to wear. Such wear is reduced by making the setting angle relatively small. In order to achieve a large stock removal notwithstanding this the setting angle may be increased for the remaining or upper portion of the cutting edge. Therefore, the invention allows to increase the service life at the cutting edge ends which as was mentioned are subjected to most stress, or to enhance productivity. These advantages may be achieved with no need to change anything to the conventional pitch on the holder tool or the seat of the cutting edge on the holder body.
In the inventive cutting tool, the cutting edges may be offset in the direction of cut or the direction of feed. If three or more cutting edge portions are contemplated an offset may be made between adjacent cutting edge portions in both the direction of cut and direction of feed. It is preferred to reduce the setting angle towards the lower portions of the cutting edge from the topmost portion. What is meant by the xe2x80x9clowerxe2x80x9d and xe2x80x9cupperxe2x80x9d ends herein is that the end of the cutting edge that plunges farthest is the lower end and, accordingly, the other end is the upper one.